On-chip battery debuts

Researchers from Hosei University in Japan
have taken a big step toward giving nano devices and biochips onboard power
supplies.

The researchers etched 200- by 100- by 2-micron trenches into silicon
chips to house tiny batteries. A micron is one thousandth of a millimeter,
and human hair is about 75 microns in diameter.

The researchers filled the trenches with a porous glass electrolyte
and electrodes made from lithium and lithium manganese oxide. The battery
produces a current of electrons when lithium ions move through the glass
from one electrode to the other. The researchers added numerous nano-sized
pores to the inside and surface of the glass, which opened more paths for
the lithium ions to travel, increasing the tiny battery's power. A nanometer
is one thousandth of a micron.

The 3.6-volt batteries deliver 34.6 watt hours per square centimeter.

The researchers are working on embedding larger numbers of smaller
batteries into silicon chips, and are working on materials that allow ions
to diffuse more efficiently. Practical miniature batteries could be ready
for use in computer chips and biochips in five to ten years, according to
the researchers.

The work appeared in the December 23, 2002 issue of Applied Physics
Letters.